Synthesis Of Dimethyl Carbonate From Oxidative Carbonylation Of Methanol Catalyzed By Copper Complexes With Phenanthroline

Dimethyl carbonate（DMC）is a green chemical product which has attracted highly attention at domestic and abroad in recent years.Several non-phosgene methods for the preparation of DMC include transesterification,methylnitrite method,alcoholysis of urea,direct synthesis from CO₂ and methanol and oxidative carbonylation of methanol.Among them,the oxidative carbonylation of methanol to DMC is the most value production because of cheap raw materials,simple synthetic route and clean.As a kind of important organic ligands,1,10-phenanthroline（phen）and its derivatives can coordinate with copper ions to form stable coordination complexes,which have been widely applied in the optics,catalysis,magnetism and sensor fields.The literature has been reported that,on the reaction of copper salt catalyzed oxidation carbonylation of methanol to DMC,the addition of phen not only greatly improves the yield of DMC,and also reduces the corrosion of the equipment.Phen has eight substitution sites,however,the influence of substituents of phen on catalytic activity has little been discussed so far.In this thesis,a series of copper complexes were prepared with methyl-substituted phen as ligands and Cu⁺/Cu²⁺ions selected as the copper sources,and characterized by elemental analysis,FT-IR,X-ray single crystal diffraction,UV-Vis spectra,thermal analysis,X-ray photoelectron spectroscopy and fluorescence.In addition,the influence of the substituent effect and structures of copper complexes on the oxidative carbonylation were also studied.（1）[Cu（phen）₂Br]₂[Cu₄Br₆]（Ⅰ）,[Cu₃I₃（phen）₂]（Ⅱ）,[Cu₃I₃（5-methyl-phen）]_n（Ⅲ）have been obtained by the solvothermal method.[Cu（phen）₂Br]₂[Cu₄Br₆]is a mixed valence Cu complexes,contains two[Cu^II（phen）₂Br]⁺cations and one tetranuclear[Cu₄^IBr₆]^2-anion.Four Cu atoms in[Cu₄^IBr₆]^2-are at corners of a tetrahedron with the side length varying from 2.6 to 2.8?,and six bromine atoms bridging along its six sides constitute an octahedron.Each of copper atoms coordinated with three bromine atoms exhibits an approximate trigonal planar coordination.The structure of[Cu（phen）2Br]2[Cu4Br6]can be described as a supramolecular network assembled via the combination ofπ-πinteractions and C-H···Br hydrogen bonds.[Cu3I3（phen）2],in which Cu and I atoms have two types of coordination environment,contains two molecules,and generates a three-dimensional supramolecular structure via?-?stacking interactions.[Cu3I3（5-methyl-phen）]n is constructed to a 1-D tape polymer with one like-drum Cu6I6hexagon prism chain combining with two 1-D zigzag chains with mphen ligands viaμ₃-I-Cu bonds.Three complexes are stable below 200℃.[Cu₃I₃（5-methyl-phen）]_n has the maximum emission band of the fluorescence at 670nm.（2）[Cu（2,9-dmphen）（SCN）]_n（Ⅳ）,[Cu（2,9-dmphen）（DMF）（SCN）₂]（Ⅴ）and[Cu（5,6-dmphen）（NCS）₂]（Ⅵ）（2,9-dmphen=2,9-dimethyl-phen;5,6-dmphen=5,6-dimethyl-phen;）have been prepared by the recrystallization.[Cu（2,9-dmphen）（SCN）]_n features one-dimensional zigzag chains with bridged thiocyanate groups.Cu（2,9-dmphen）（DMF）（SCN）₂]is constructed to a three-dimensional supramolecular structure via C-H???S hydrogen bond and?-?stacking interactions.[Cu（2,9-dmphen）-（SCN）]n exhibits the higher thermal stability than[Cu（2,9-dmphen）-（DMF）（NCS）2],and has the maximum fluorescence emission at 603nm.In[Cu（5,6-dmphen）（NCS）₂],one isothiocyanate ion is coordinated to Cu atom,and the other is used as a bridging ligand to construct the complex into a one-dimensional zigzag-chain structure.（3）The Cu（L）Br₂（L=2-methyl-phen,4-methyl-phen,5-methyl-phen,2,9-dimethyl-phen,4,7-dimethyl-phen,5,6-dimethyl-phen）complexes have been synthesized by precipitation method with L as the ligand and CuBr₂ as the copper resource.When Cu（L）Br2 were used as the catalysts,the activity of Cu（2-methyl-phen）Br2 and Cu（2,9-dimethyl-phen）Br₂ mainly influences by the steric hinder effect of the methyl,while the electronic effect of the methyl is dominant for Cu（5-methyl-phen）Br₂,Cu（4-methyl-phen）Br2,Cu（5,6-dimethyl-phen）Br2 and Cu（4,7-dimethyl-phen）Br2;the catalytic performance of the catalyst containing the mono-methyl group is higher than that of the corresponding catalyst with two methyl groups,and Cu（5-methyl-phen）Br2givesthehighestcatalyticperformance.When Cu（5-methyl-phen）Br₂ was used as the catalyst,under the conditions of concentration of the catalyst in methanol of 0.011mol·L^-1（based on methanol）,reaction temperature130°C and reaction time 4h,the turnover number（TON）and selectivity for DMC were up to 67.2 and 96.9%,respectively.（4）In the[Cu₄Br₆]^2-ion of[Cu（phen）₂Br]₂[Cu₄Br₆],four copper atoms constitute a distorted tetrahedron,each of which exhibits approximate trigonal planar coordination through three bromine atoms,and six bromine ligands lie on the six edges of the tetrahedron to bridge four copper atoms.This bridged structure provides an excellent environment for the oxidative carbonylation of methanol.Under optimized reaction conditions of catalyst amount of 0.011mol/L,5 h and 120°C,the TON and DMC selectivity are up to 54.7 and 97.5%,respectively.And[Cu（phen）2Br]2[Cu4Br6]can be reused at least eight recycles with a slight loss of activity and selectivity.（5）In[Cu（phen）I]_n,[Cu（phen）I]₂,[Cu₃I₃（phen）₂],[Cu₃I₃（5-methyl-phen）]_n and[Cu₃I₃（phen）]_n,Cu centers exhibit the very high activity in the reaction of oxidative carbonylation of methanol when the Cu???Cu distance is shorter than 4?.On the contrary,Cu centers show the low activity.Among them,the activity of[Cu（phen）I]₂ is the highest.Under optimized reaction conditions with[Cu（phen）I]₂ as the catalyst,reaction time of 5h,reaction temperature of 120°C and concentration of the catalyst in methanol of0.011mol·L^-1（based on methanol）,the TON is up to 63.3.When the catalyst is reused for10 times,the TON of about 60.0 is kept with above 99.0%selectivity of DMC.